Function and functional groupings of the complex mouth apparatus of the squat lobsters Munida sarsi Huus and M-tenuimana GO Sars (Crustacea : Decapoda)

Like all other decapods, the anomuran squat lobsters Munida sarsi and M. te nuimana have a mouth apparatus composed of six pairs of mouthparts plus lab rum and paragnaths (upper and lower lips). To study the functional signific ance of this complexity, we examined the mouthparts with scanning electron microscopy and also observed their function directly, under laboratory cond itions, using macro-video equipment. No differences were found between the two species. The movement patterns of the mouthparts are described in detai l and illustrated as serial drawings. Proceeding from maxillipeds 3 towards the mandibles, the movement pattern gets increasingly stereotypical, with the mandibles performing but a single movement in a medio-lateral plane. Fr om morphology, the mouthparts are subdivided into 20 parts, but from the fu nctional analyses the 20 parts form 8 functional groups: 1, transporting mo uthparts (maxilliped 2 endopod and maxilliped 3 endopod); 2, transporting-a ligning mouthparts (maxilliped 1 basis); 3, sorting-aligning mouthparts (ma xilla 1 basis and maxilla 2 basis); 4, current-generating mouthparts (flage lla of maxilliped 2 and maxilliped 3 exopods); 5, cutting-crushing mouthpar ts (incisor and molar processes, labium, and mandibular palp); 6, ingesting mouthparts (maxilla 1 coxa, maxilla 2 coxa, and maxilliped 1 coxa): 7, res piratory mouth-parts (scaphognathite, maxilliped 1 epipod, and maxilliped 2 and maxilliped 3 exopods); and 8, dorso-ventral mouthparts (maxilla 1 endo pod, maxilla 2 endopod, maxilliped 1 endopod, and maxilliped 1 exopod). The se groupings apply mostly to the processes of food handling and have little significance with respect to grooming. When comparing our results to the l iterature on other decapods, we found much resemblance to conditions in oth er anomurans.